Various processes of use of copper and cobalt catalysts have been disclosed in the patent literature. In the process for synthesizing alcohols according to U.S. Pat. No. 4,122,110, the catalysts are directly placed into the synthesis gas.
According to the process disclosed in the French patent application No. 2 523 957, the catalysts are preliminarily reduced. This reduction may be achieved, according to this patent, for example in a single step, by means of a mixture of inert gas with at least one reducing compound, in a molar ratio "reducing gas/reducing gas+inert gas" from 0.001:1 to 1:1, the reducing gas being selected from the group consisting of hydrogen, carbon monoxide, C.sub.1 and C.sub.2 alcohols and aldehydes, the reduction being performed at a temperature from 100.degree. to 750.degree. C., preferably from 150.degree. to 550.degree. C. and, for example, by 10-hour steps from 170.degree. C. to 240.degree. C., under a pressure from 0.1 to 10 megapascals (MPa), preferably 0.1-6 MPa and for example at atmospheric pressure (0.1 MPa).
Another method of preliminary reduction of the catalysts according to this patent application consists of proceeding in at least two successive steps. In this embodiment, the first reduction step is conducted at a temperature from 150.degree. to 250.degree. C. with a molar ratio "reducing gas/reducing gas+insert gas" from 0.001:1 to 0.1:1, said first step being continued until the concentrations of reducing gas at the input and the output of the reactor be the same.
Then, in a second step, the temperature is increased up to a value ranging from 220.degree. to 750.degree. C., preferably from 240.degree. to 550.degree. C., the molar ratio "reducing gas/reducing gas+inert gas" being from 0.01:1 to 1:1. During said second step, it is generally advantageous to use a higher concentration of reducing gas than in the first step.
Another process of use of catalysts for synthesizing alcohols, particularly higher alcohols, has been disclosed in U.S. Pat. No. 4,477,594.
The process disclosed in this patent concerns the use of catalysts for synthesizing C.sub.2 -C.sub.9 saturated aliphatic alcohols from synthesis gas, said catalysts comprising oxides of copper, zinc, aluminum, potassium and one or two metals selected from the group consisting of chromium, manganese, cerium, cobalt, thorium and lanthanum.
This process comprises a first step of partial activation of the catalyst by contacting said catalyst with a gas stream comprising hydrogen and at least one inert gas, said gas stream having a space velocity up to 5000 liters per hour and per kilogram of catalyst; a second activation step wherein the catalyst obtained in the first step is contacted with hydrogen and carbon monoxide, the H.sub.2 /CO volume ratio being from 0.5:1 to 4:1, the temperature from 200.degree. to 450.degree. C. and the pressure from 35 to 200 atmospheres, said H.sub.2 +CO mixture having a space velocity from 1000 to 20 000 liters per hour and per kilogram of catalyst and said second step being continued until at least 500 000 liters of gas per kilogram of catalyst have been in contact with said catalyst; a third step of synthesizing saturated aliphatic alcohols, consisting of contacting the activated catalyst obtained at the end of the second step with a synthesis gas containing hydrogen and carbon monoxide in a ratio by volume from 0.5:1 to 4:1, at a space velocity from 1 000 to 20 000 liters per hour and per kilogram of catalyst, at a temperature from 200.degree. to 450.degree. C. and under a pressure from 35 to 200 atmospheres (3.5 to 20 MPa).
This patent thus discloses a process wherein the catalyst is subjected to a reduction with a gas mixture containing hydrogen and an inert gas and then to the synthesis conditions. Then only after a certain operating period is the catalyst employed to obtain products. The use of the catalysts according to one of the above-described methods, however, does not always provide for a satisfactory selectivity by weight to alcohols S.C.sub.2.sup.+ OH (alcohols having 2 carbon atoms or more) and/or a sufficient selectivity to total alcohols (SA) and/or an acceptable productivity by weight.
According to the present invention, a new procedure has been discovered for using catalyst for synthesizing higher saturated aliphatic alcohols, said procedure providing mostly for a substantial increase in one or more of the deserved relationships performances of the reaction: weight productivity (P) to alcohols, selectivity (S.sub.A) to total alcohols, and selectivity by weight to higher alcohols (S.C.sub.2.sup.+ OH).
The process according to the present invention also provides, in particular, for at least a partial improvement of the selectivity and/or productivity of a catalyst used over a relatively long period and whose activity, at the end of this operating period, is decreased as compared with its initial activity and/or whose selectivity decreases in such proportions that it is no longer possible to continue the synthesis under acceptable economic conditions and/or the desired products are no longer formed in sufficient proportions.
The process according to the invention thus avoids the need to replace the used catalyst with a fresh catalyst. A satisfactory selectivity and/or activity is restored to the used catalyst according to the present invention. Thus the used catalyst may continue to be used over a new operating period.